Left atrial transport in mitral stenosis.

Active left atrial transport was examined acutely in five patients with mitral stenosis and sinus rhythm. To observe the effect of active left atrial contraction on subsequent left ventricular output, the timing of atrial contraction with respect to ventricular contraction was varied. Atrioventricular (A-V) dissociation produced by right ventricular pacing was used to change continually the relationship of left atrial (LA) to left ventricular (LV) contraction. Measurements of each beat included mitral valve gradient, left ventricular ejection time (LVET), and left ventricular peak-systolic pressure (LVPSP). The diastolic gradient was used to calculate diastolic flow per beat after the area of the stenotic mitral orifice had been previously determined. Calculated diastolic flow increased significantly (24%) as did the parameters of left ventricular output, LVPSP and LVET (P < 0.005 for both), when atrial contraction was optimally timed. Cumulative effects were observed when a series of well-placed or poorly placed atrial contractions occurred. The method documents change in LV output which depends on appropriate timing of LA contraction that may not have been seen with a steady-state approach.